Intelligent Reflecting Surface Secure Backscatter Communication Without Eavesdropping CSI

This letter presents an intelligent reflecting surface secure backscatter communication system. In this system, an IRS, as a backscatter device, leverages the signals from a power beacon (PB) as carriers to send confidential messages to a legitimate user. Meanwhile, an eavesdropper with unknown channel state information (CSI) attempts to intercept the messages. A power minimization scheme using the block coordinate descent and the semidefinite program methods is developed to realize secure transmission. This scheme jointly optimizes the PB’s beamformer and the IRS’s reflection coefficient to elevate the secrecy rate. Simulation results demonstrate that the optimization scheme can achieve secure communication in the proposed system.